extrapolation

1.To infer (values of a variable in an unobserved
interval) from values within an already observed interval.

2a. to project, extend or expand (known data or experience) into an area not known or experienced so as to arrive at a usually conjectural knowledge of the unknown area (extrapolates present trends to construct an image of the future).

2b. to predict by projecting past experiences or known data (extrapolate public sentiment on one issue from known public reaction on others